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Obesity is a major global public health concern. Immune responses implicated in obesity also control certain infections. We investigated the effects of high fat diet (HFD)-induced obesity (DIO) on infection with the Lyme disease bacterium Borrelia burgdorferi in mice.

DIO was associated with systemic suppression of neutrophil- and macrophage-based innate immune responses. These included bacterial uptake and cytokine production, and systemic, progressive impairment of bacterial clearance and increased carditis severity.

B. burgdorferi-infected mice fed normal diet also gained weight at the same rate as uninfected mice fed HFD, Toll-like receptor 4 deficiency rescued bacterial clearance defects, which were greater in females than males, and killing of an unrelated bacterium (Escherichia coli) by bone marrow-derived macrophages from obese, B. burgdorferi-infected mice was also affected.